Fluids being produced from oil wells may comprise a mixture of fluid components like oil, water, gas, and sand etc., which are commonly referred to as fluid phase, where the percentage fraction of each respective fluid component may vary from one oil field to another, and also during the operational lifetime of the oil from a same oil well. It is for example common to have an increase in water content from the oil well towards the end of the production life time of the well.
Separation of fluid components may be necessary to be able to provide further processing of the oil and gas in a refinery for example. However, the requirement of providing separation is not always a specific requirement. Sometimes it is only necessary to separate water from the oil, either as a course separation process, or with a higher demand on separation results and/or efficiency. There are some proposals for separators in prior art providing separation of water from fluids being produced from oil wells. A common technique is to utilize the known fact that water has a higher density than oil, and therefore it is possible to use gravity as a separating force. A common known separator arrangement is using a large tank where the fluids from the oil well are kept still for a time period. During this time period the gravity forces separate the oil and water, and the water is piled up at the bottom of the tank from where it can be removed, and gas may be piled up at the top of the tank above the oil since gas has a lower density than oil and water. Sand may also be piled up in the bottom of the tank together with the water.
It is also known more active types of separators, for example a class of separators denoted cyclone separators. The patent application EP0266348 A1 from 17 Jun. 1985 disclose a cyclone separator comprising a separating chamber (1), (2) (3); at least one inlet (8), for introducing feed to be separated into the cyclone separator and at least two outlets (4), (10), for discharging material from the separating chamber. The separator comprises at least one generally circumferential slot (20), disposed in the wall of the separating chamber downstream of each inlet slot (20), leading to or communicating with an exit from the separating chamber.
The gravitational separator tank installations are rather large and can usually only be located at centrally located places on land. Especially, in connection with oil production from the sea bed this has been regarded as an unfavourable solution. The paten publication U.S. Pat. No. 8,002,121 with priority from 15 Nov. 2004, by Michel Berard et al., addresses this problem by arranging an in-line flow separator being installable on a sea bed comprising an uphill section of a pipeline connected to a well head, where a first liquid (oil) and a second denser liquid (water) may flow through the separator from the bottom of the separator to an uphill located outlet opening. The second liquid forms a sump due to gravitation extending uphill from the bottom of the separator to an interface between the water and oil. An outlet in the bottom of the separator makes it possible to remove the water (the second liquid) collected in the sump. A series of sensors are arranged in the uphill section to monitor the position of the interface between the water and the oil.
The international patent application WO 02/01044 by Skovholt et al. discloses an inclined gravitational separator having an inner pipe arranged inside an outer pipe. A pipe carrying fluids from an oil well head are arranged to be in fluid communication with the inner pipe via a tube joint located in a bottom surface of the inclined separator. The inner pipe has a plurality of perforations (or holes) in the inner pipe walls, and due to gravity water (and sand if present) in the fluid from the well head will fall through these openings, and will be collected in a sump in the bottom of the outer pipe. The separated oil will flow out of the inner pipe from an opening in a top section of the separator. The pressure from the oil well drives the fluids through the separator system.
However, the plurality of openings, for example round holes, has a tendency to induce turbulence in the streaming flow out from the inner pipe into the outer pipe which may require slowing down the flow of fluids and which may also provide an unfavourable mixing of fluid components, especially in the interface between water and oil. This condition can be difficult to handle if the fluid from the well head is under high pressure. Further, if the speed of the flow of fluid components in the outer pipe is too high, the streaming of fluids past the outside of the openings in the wall of the inner pipe may provide a suction force due to the Venturi effect, as known to a person skilled in the art. Therefore, it is possible that the separator under certain conditions may extract (pump) water from the sump into the stream of fluids in the inner pipe instead of separating for example the water from the oil. Therefore, it may be necessary to reduce the velocity of fluid streaming in the arrangement. According to the teaching of Skovholt et al. this can be achieved with valves that are controlled in a feedback loop, wherein control signals are generated proportional to signals from respective pressure transducers, for example.
It may further be a problem that the interface between the water and oil in the separator may be a diffuse interface (no distinct border line between the fluids) and also that the interface may be located at different levels relative to for example the bottom of the separator. If the interface is too close to the bottom the number of openings in the inner pipe walls the water may fall through due to gravitation will be less compared to a situation where the interface is higher up in the inclined separator. Therefore, the separation capacity may be variable due to for example variable flow rates.
In the patent application WO 02/01044 it is disclosed that a number of separator arrangements may be arranged in parallel to increase the separator capacity or in series to obtain a gradual separation through a series of connected separators. However, due to the possible suction problem discussed above, the flow rate through the respective separators should probably be reduced thereby limiting the total capacity of the arrangement even when there is a plurality of separators arranged in parallel.
Processing of fluids in other processing stages, or at other locations, may dictate the number of separated phases that are needed. The composition and respective percentage fraction of volume of gas, oil, water and sand etc. will vary from the start of production towards the end of production from an oil well. Further, it should also be possible to provide different separation schemes with respect to how many components or phases that it is intended to be separated during different stages of the production lifetime of an oil well. For example, an oil and gas mixture can be separated from water which implies a two phase separator. Another example can be separation of an oil and sand mixture from separated gas and separated water, which implies a three phase separator. All the fluid phases may also be separated which implies for example a four phase separator. In addition, the volume of each phase or fluid component in the fluid mixture will influence the capacity of the system with respect to the separator sections handling each respective fluid component. It is also beneficial to be able to configure which fluid phases that should remain together after passing the separator system if not all phases are separated, for example oil and water, oil and gas etc.
Further, it may be advantageous to be able to combine more separators based on different physical separation principles, for example cyclone separators and/or gravitational separators in an optimized configuration.
There are also other further issues to take into consideration. For example, variable flow rates, oil, water, slugs etc. may provide mechanical stress and shaking of the installation as known to a person skilled in the art.
Hence, an improved method for adapting and manufacturing a separator system to actual conditions would be advantageous.
It is an object of the present invention to provide an alternative to the prior art.
In particular, it may be seen as an object of the present invention to provide an adapted separator system for oil well fluids that solves the above mentioned problems of the known art with a separator system that is may be adapted to a plurality of different oil production requirements during all stages of the lifetime of an oil well.